1. Field of the Invention
This invention relates to an anti-skid brake control system for automobiles.
2. Description of the Prior Art
An anti-skid brake control system for automobiles usually includes a speed sensing device for detecting wheel rotational speed and an actuator which controls the brake circuit between the master and wheel brake cylinders to reduce and increase the brake pressure at the wheel brake cylinders in response to signals from the speed sensing device. More particularly, when the sensor detects a locking tendency at the rear wheels, the computer actuates a fluid operated actuator to disconnect communication between the master cylinder and wheel brake cylinders and at the same time increase the volume of the brake circuit at the wheel brake cylinders to thereby reduce the braking pressure. Then when the sensor detects no further locking tendency of the wheels due to the pressure reducing actuation of the actuator, the computer discontinues actuation of the fluid actuator to thereby regain the brake pressure at the wheels. The rapid repetitions of this increase and decrease of wheel brake pressure for a very period of time during brake operation will protect the wheels from locking because of the excess braking force and because of slippery road conditions and therefore protect the vehicle from skidding which may naturally result in a serious accident.
The above type of anti-skid brake control system is disclosed, for example, in U.S. Pat. No. 3,877,756. Although this type is very reliable, it is necessary to install a relatively large size actuator within the brake circuit and to provide a fluid source for actuating the actuator.
Another related U.S. Pat. No. 3,549,211 discloses a similar anti-locking control system wherein there is no conventional actuator used. However, this system requires a pump for regaining pressure when a locking tendency ceases.
Further, U.S. Pat. No. 3,425,751 discloses a similar system. According to this system, an additional locking tendency may occur during pressure regaining operation.